In evaluating persons for physical health and the diagnosis of certain medical conditions, there is often a need to assess the weight of the persons continuously throughout their daily routines. For example, it may be useful in the diagnosis of certain medical conditions (e.g., Parkinson's, congestive heart failure, liver disease, psychosomatic disorders, and the like) to continuously evaluate a weight change pattern of a person. Further, such analysis may be useful in the rehabilitation of injured or disabled individuals. The analysis of weight change patterns may be useful not only for persons but animals as well, as it may assist in the evaluation of animal performance for competitive applications or for diagnosing or otherwise assisting with rehabilitation of animals. In order to continuously assess weight changes, it is first necessary to determine the weight of a person or animal while they are moving.
Conventionally, determining the weight of a person while moving has been highly complicated and subject to error. To measure the weight of a person while moving, conventional approaches have used force sensors to measure the force exerted by each foot. FIG. 1 shows an exemplary graph illustrating the forces detected by each foot throughout a walking cycle of a person. Notably, the forces detected by these force sensors are not directly related to the weight of the person. Rather, as shown, due to the motion of the person, the forces detected by a sensor under each foot experience peaks and valleys that fluctuate throughout the walking cycle (e.g., heel contact, heel-to-toe roll, and push-off). This is due to the shift in center of mass (CoM) of the person during the walking cycle and the acceleration of the CoM between these shifts. FIG. 2 illustrates this phenomenon, where the CoM of the person shifts up and down throughout the walking cycle, and accelerates between these shifts.
With this in mind, conventional approaches use a CoM acceleration sensor in order to determine the best point to measure (BPM) the force exerted by each foot to obtain the most accurate weight of the individual while walking. In particular, the CoM acceleration sensor is used to determine when a vertical acceleration of the CoM of the person is near zero, at which point the force sensors for each foot accurately reflect the weight of the person. Such an approach is subject to error, however, because it requires very accurate placement of the CoM acceleration sensor and synchronization between the CoM acceleration sensor and the force sensors at each foot. In addition, the commonly used sensors of the conventional methods use motion sensors that are based on the micro-electromechanical design principles of Inertial Motion Units (IMUs). Such IMU sensors are known to be prone to significant measurement errors due to the repeated impact of the foot on the walk surface.
Accordingly, there is a need for an apparatus and method for accurately measuring the weight of persons or animals while walking with reduced complexity.